Method of applying insulated pieces to carbon brushes.



v c. Y.KNI.GH.T&1W-. N. WILSON.

METHOD OF APPLYING INSULATED ,PIECE'S T0 OARBONBRUSHES.

APPLICATION. HLED NOV. 30,1918. 1 2 9 9 5 Patented Apr. 1,1919.

wr I 7 E FzgZ UNITED sTATEs PATENT OFFICE,

CECIL YOUNG KNIGHT AND WILLIAM NORMAN WILSON, OF BATTERSEA, LONDON,

ENGLAND, ASSIGNORS TO THE MORGAN CRUCIBLE COMPANY, LIMITED, OF BAT- 'IEBSEA, LONDON, ENGLAND.

METHOD OF APPLYING INSULATED PIECES T0 CARBON BRUSHES.

' Patented Apr. 1, 1919.

Application filed November so, 1918. Serial No. 264,809.

To all whom it may concern:

Be it known that we, CECIL YOUNG KNIGHT and'VVILLIAM NORMAN WILSON, subjects of the King of Great Britain, both residing at Battersea, London, England, have invented a new and useful Method of Applying Insulated Pieces to Carbon Brushes, of which the following is a specification.

This invention relates to carbon brushes for use in connection with dynamo-electric generators or electric motors, and to that class of such brush designed to be retained in contact with the commutator by means of a finger or like pressure device acting against one end thereof, such end, for convenience of description, being hereinafter referred to as the top of the brush.

It is found in practice that the vibration resulting from the running of an electric generator or motor sets up a hammer action I of the finger or the like and tends to abrade or wear away the top of the brush. Erosion or pitting of the'brush and the finger also takes place, this being due to the passage of current between the brush and finger.

To counteract the effect of wear a plate of metal or other material is sometimes fixed to the top of the brush, or a soft cushion is interposed between the finger and the brush, and, in order to prevent the passage of current between the finger and brush, and avoid the erosion or .pitting caused thereby, a piece of insulating material is fixed either to the end of the finger, which makes contact with the brush, or to the top of the brush itself.

The use of such a plate of material, however, is objectionable in that under the influence of vibration it is liable to become de tached from the brush.

. According to the present invention 'instead of applying a piece or layer of insulating material in a solid form we apply it as a plastic composition which is molded upon or otherwise applied to the brush, and

subsequently hardened thereon, in such a manner as to form an integral part of, or to be practically homogenous with, the material of the brush.

The composition which we make use of is advantageously composed of an aggregate of powdered mica, sawdust or other suitable material of a non-conducting nature to which is added a binding material, such as sodium silicate or a condensation product Powdered mica 15 parts, Sodium silicate of density of 70 Baum 22 parts.

This composition is applied to the brush in a mold or otherwise as may be most convenient and is subsequently allowed to harden, which hardening may be accelerated by stoving.

It is to be understood, however, that the invention is not limited to the use of the insulating composition before described. For instance, vulcanized fiber, vulcanite or like material can be made use of, the ingredients constituting which are applied in their unvulcanized condition and vulcanized in situ. Such insulating material may be applied to the carbon in a mold and vulcanized before removal from thelatter.

The surface of the brush upon which the insulating material is to be applied may be provided with projections or recesses to constitute a key with which the plastic insulating material will interlock. When, however, the plastic material is of a sufficiently adhesive nature, such a key can be dispensed with; furthermore, whether a key is used or not, and even when the plastic material is of an adhesive nature, a coatingor layer of a suitable adhesive, which will become thoroughly hard, may be applied between the wherein an undercut circular recess ti formed in the top of the loloclr.

Fi 1 0 shows an arrangement wherein. a key 1s provided by forming in the block holes 6, e inclined in opposite directions.

It will be understood, however, that, Whatever may be the form of key used, when the plastic insulating material is applied and has hardened, such insulating material cannot be separated from the carbon without breaking one or the other as the two will be locked together, Furthermore, brushes having insulating material applied as hereinbefore described can be ground or otherwise manipulated as a whole to fit the holders in which they are to be used.

Metallic pig-tails f or other conductors can be applied either before or after the application of the insulating material.

in some cases metal fittings may be wholly or part1ally embedded in the plastic composition so that such metal fittings are not in electrical connection with the body of the brush; for example, a strip of metal of channel or U-shaped section can he embedded in the composition so that the lateral walls of such strip form a channel into which the pressure finger of the brush holder may enter the said lateral walls pre venting the finger from slipping over the edge of the brush, Also the plastic compe= naeaeee providing the carbon brush with keying means, placing the insulated piece on said brush in plastic condition and interlocking the same to the keying means, and =permit-' ting said insulated piece to harden.

2-. A method of applying an insulated piece to a carbon brush, which consists in providing the carbon brush with a recess having undercut side walls, placing the insulated piece in said recess in plastic condition, and permitting said insulated piece to 5' harden in said recessv 3. A method of applyingan insulated. piece to a carbon brush, which consists in providing the brush with keying means, placing plastic insulating material, composed of an aggregate of non-conducting nature and a binding material, in engagement with said keying means, and permitting said material to harden CECIL YGUNG KNIGHT WILLIAM NURMAN WiiiStllla 

